Summary Questions Biological Molecules

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Large molecules often contain carbon. Explain why this is.
Carbon atoms readily link to one another to form a chain.
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What is a poymer?
A molecule that is made up of many similar repeating units.
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Why does Benedict's reagent turn red when heated with a reducing sugar?
Sugar donates electrons that reduce blue copper (II) sulfate to orange copper (I) oxide.
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Suggest a way, other than comparing colour changes, in which different concentrations of reducing sugar could be estimated.
Dry the precipitate in each sample and weigh it. The heavier the precipitate the more reducing sugar is present.
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Explain why it is not possible to distinguish between very concentrated samples, even when their concentrations are different.
Once all the copper (II) sulphate has been reduced to copper (I) oxide, further amounts of reducing sugar cannot make a difference.
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Which carbohydrate(s) stains deep blue with iodine solution?
Starch
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Which carbohydrate(s) is known as 'animal starch?
Glycogen
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Which carbohydrate(s) is found in plants?
Cellulose, starch, alpha and beta glucose
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Which carbohydrate(s) are polysaccharides?
Starch, cellulose and glycogen
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Which carbohydrate(s) is a monosaccharide found in starch?
Alpha glucose
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Which carbohydrate(s) has a structural function?
Cellulose
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Which carbohydrate(s) can be hydrolysed?
Starch, cellulose, glycogen
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Which carbohydrate(s) easily moves in and out of cells by facilitated diffusion?
Alpha and beta glucose
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List two differences between a triglyceride molecule and a phospholipid molecule.
Triglycerides have 3 fatty acids/no phosphate group, whereas phospholipids have 2 fatty acids/a phosphate group. Triglycerides are non-polar, whereas phospholipids have a hydrophilic head and hydrophobic tail.
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Organisms/parts of organisms that move use lipids rather than carbohydrates as an energy store. Suggest one reason why this is so.
Lipids provide more than twice as much energy as carbohydrate when they are oxidised. If fat is stored, the same amount of energy can be provided for less than half the mass. It is therefore a lighter storage product - a major advantage if mobile.
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List the four different components that make up an amino acid.
Amino group (-NH2), carboxyl group (-COOH), hydrogen atom (-H), R group
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Why does the quaternary structure of collagen make it suitable for use as a tendon?
It has three polypeptide chains wound together to form a strong, rope-like structure that has strength in the direction of pull of a tendon.
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Suggest how the cross-linkages between the amino acids of polypeptide chains increase the strength and stability of a collagen fibre.
They prevent the individual polypeptide chains from sliding past one another and so they gain strength because they act as a single unit.
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The points where one collagen molecule ends and the next begins are spread throughout the fibre in different places. Explain why this arrangement is necessary for the efficient functioning of a tendon.
The junctions between adjacent collagen molecules are points of weakness. If they all occurred at the same point in a fibre, this would be a major weak at which the fibre might break.
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Explain why enzymes are effective in tiny quantities.
They are not used up in the reaction and so can be used repeatedly.
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Outline why changing one of the amino acids that make up the active site could prevent the enzyme from functioning.
The changed amino acid may no longer bind to the substrate, which will then not be positioned correctly, if at all, in the active site.
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Explain why changing certain amino acids that are not part of the active site prevents the enzyme from functioning.
The changed amino acid may be one that forms hydrogen bonds with other amino acids. If the new amino acid does not form hydrogen bonds the tertiary structure of the enzyme will change, including the active site, so that the substrate no longer fits.
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Explain why the induced fit model is a better explanation of enzyme action than the lock and key model.
It more clearly matches modern observations such as enzyme activity being changed when molecules bind at sites other than the active site. This suggests that enzyme molecules change shape when other molecules bind to them. Enzymes flexible, not rigid
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Explain why enzymes function less well at lower temperatures.
To function, enzymes must physically collide with their substrate. Lower temperatures decrease the kinetic energy of the enzymes and substrates, which then move around less quickly. They hence collide less often and therefore react less frequently.
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Explain how high temperatures may completely prevent enzymes from functioning.
The heat causes hydrogen and other bonds in the enzyme molecule to break. The tertiary structure of the enzyme molecule changes, as does the active site. The substrate no longer fits the active site.
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Other cards in this set

Card 2

Front

What is a poymer?

Back

A molecule that is made up of many similar repeating units.

Card 3

Front

Why does Benedict's reagent turn red when heated with a reducing sugar?

Back

Preview of the front of card 3

Card 4

Front

Suggest a way, other than comparing colour changes, in which different concentrations of reducing sugar could be estimated.

Back

Preview of the front of card 4

Card 5

Front

Explain why it is not possible to distinguish between very concentrated samples, even when their concentrations are different.

Back

Preview of the front of card 5
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